Recording medium

1. A recording medium comprising: a guide layer on which a guide track or guide tracks for tracking are formed; and a plurality of recording layers laminated on the guide layer, wherein, a same mark group is formed in a same rotational phase position of each of at least two guide tracks out of a plurality of guide tracks which are included in a beam spot at the same time which is formed on the guide layer by guide laser light irradiated on the guide layer, the mark group includes a pair of record marks which are shifted by a predetermined distance toward a right side and a left side, respectively, from a track center of the each guide track, and a depth of the pair of record marks is less than λ/6n, where λ is a wavelength of the guide laser light and n is a substrate refractive index of the recording medium.

2. A recording medium comprising: a guide layer on which a guide track or guide tracks for tracking are formed; and a plurality of recording layers laminated on the guide layer, wherein, a same mark group is formed in a same rotational phase position of each of at least two guide tracks out of a plurality of guide tracks which are included in a beam spot at the same time which is formed on the guide layer by guide laser light irradiated on the guide layer, the mark group includes a pair of record marks which are shifted by a predetermined distance toward a right side and a left side, respectively, from a track center of the each guide track, and a depth of the pair of record marks is λ/8n, where λ is a wavelength of the guide laser light and n is a substrate refractive index of the recording medium.

3. A recording medium comprising: a guide layer on which a guide track or guide tracks for tracking are formed; and a plurality of recording layers laminated on the guide layer, wherein, a same mark group is formed in a same rotational phase position of each of at least two guide tracks out of a plurality of guide tracks which are included in a beam spot at the same time which is formed on the guide layer by guide laser light irradiated on the guide layer, the mark group includes a pair of record marks which are shifted by a predetermined distance toward a right side and a left side, respectively, from a track center of the each guide track, and the mark group includes (i) a mark group including the pair of record marks and (ii) a mark group obtained by combining the pair of record marks with another record mark located on the track center of the each guide track.

4. The recording medium according to claim 3 , wherein the mark group including the pair of record marks is a mark group indicating predetermined bit data to be recorded into the guide layer, and the mark group obtained by combining the pair of record marks with another record mark located on the track center is a mark group indicating synchronous data for synchronization when the bit data is read.

5. A recording medium comprising: a guide layer on which a guide track or guide tracks for tracking are formed; and a plurality of recording layers laminated on the guide layer, wherein, a same mark group is formed in a same rotational phase position of each of at least two guide tracks out of a plurality of guide tracks which are included in a beam spot at the same time which is formed on the guide layer by guide laser light irradiated on the guide layer, the mark group includes a pair of record marks which are shifted by a predetermined distance toward a right side and a left side, respectively, from a track center of the each guide track, and the mark group is formed by combining the pair of record marks such that an average value of a signal level of a push-pull signal is zero, the push-pull signal being obtained by irradiating the guide laser light onto the mark group.

6. A recording medium comprising: a guide layer on which a guide track or guide tracks for tracking are formed; and a plurality of recording layers laminated on the guide layer, wherein, a same mark group is formed in a same rotational phase position of each of at least two guide tracks out of a plurality of guide tracks which are included in a beam spot at the same time which is formed on the guide layer by guide laser light irradiated on the guide layer, the mark group includes a pair of record marks which are shifted by a predetermined distance toward a right side and a left side, respectively, from a track center of the each guide track, the guide tracks include groove tracks and land tracks alternately formed, a mark group is formed in a same rotational phase position of each of a plurality of groove tracks which are included in the beam spot, the mark group including a pair of record marks which are shifted by a predetermined distance toward a right side and a left side, respectively, from a track center of the each groove track, and a mark group is formed in a same rotational phase position of each of a plurality of land tracks which are included in the beam spot, the mark group including a pair of record marks which are shifted by a predetermined distance toward a right side and a left side, respectively, from a track center of the each land track.

7. The recording medium according to claim 6 , wherein the mark group formed on the land track is formed as a mark group which is formed simultaneously with formation of two groove tracks adjacent to the land track.